The present invention relates to a nonreturn or check valve for use in medical fluid applications.
It is the state of the art (for example, as shown in DE 40 39 814 A1 and U.S. Pat. No. 4,966,199) to design a nonreturn valve with a two piece housing providing a first pipe connector and a second pipe connector between which a diaphragm made of a flexible material is located. Upon overpressure in the first or second pipe connector, the diaphragm is lifted from its sealing seat and a flow passage is created. Respective overpressure on the side opposite the sealing seat forces the diaphragm quickly and safely against the sealing seat, thus shutting the flow passage.
The solution shown in DE 40 39 814 A1 aims at improving the nonreturn valve through increased independence from manufacturing tolerances, and at achieving safe opening and shutting at lowest pressure differences. The design features a diaphragm with a circumferential section clamped into the housing, a central sealing section, and a thinner annular wall connecting both sections. Sealing effects, as well as opening times, depend on the way the diaphragm is clamped, which cannot be done reliably when the manufacturing tolerances are too high. The diaphragm can be subjected to an external, radial load to increase the opening force, but this does not help to improve the operational characteristics. In the known design, a high pretension can only be achieved by providing the diaphragm with a specifically designed thinner annular wall. In the known solution, the pretension is in a section of the diaphragm with reduced wall thickness; the absolute pretension may therefore not be very high.
The second solution shown in U.S. Pat. No. 4,966,199 features a loose, unperforated diaphragm, i.e. the circumference of the diaphragm is not clamped, and central and border sections move axially according to the operating conditions. Special elements are therefore provided to support the diaphragm in a centered position. Opposite flow directs the reflux toward the center of the downstream surface of the diaphragm. The reflux lifts the diaphragm from the supporting edges, over which it is bent during forward flow, and seals it off against a concave sealing surface. A flow converter protects this diaphragm against high pressure during forward flow, and the concave sealing surface protects it against high reflux pressure. Upon absence of forward or backward fluid pressure, the diaphragm assumes a neutral position where it forms a line contact with a curved, convex surface on the upstream side of the diaphragm, thus shutting off any reflux.
Such nonreturn valves are used in medical engineering for ducts in infusion systems, diagnosis equipment, syringes, intravenous tubes, etc. The following requirements must be met my such nonreturn valves:
a) the nonreturn valves must shut off very safely within fractions of a second to avoid any reflux of fluids contaminated with undesired agents; and PA1 b) their protection must be not only economical but with a high statistical safety.
There are strict laws requiring thorough examinations to ensure a consistent and long-lasting operational safety. The operational safety of such nonreturn valves is checked by the German Technical Surveyance Institution (Technischer Uberwachungsverein TUV), for example, permitting the medical application of such nonreturn valves only after thorough examination.
The invention provides a solution to the problem of creating a quickly and safely shutting nonreturn valve by exerting a radial tensile stress on the diaphragm.
The advantages achieved through this invention are in particular the quicker and equally safe operation of the nonreturn valve permitted by suitable adjustment of the tensile strength. Furthermore, reaction time and opening pressure can be influenced by adjusting the tensile stress through geometry modification. The production of the individual parts is extremely cost-efficient and statistically safe. For transmitting the increased pretension, the diaphragm border has a bulge which is simple to produce by injection molding, and favorably the wall thickness of the diaphragm center is not reduced. These two features are of advantage for the safe clamping, and the transmission of high tensile forces, respectively.
A favorable design example of the invention features the two valve shells with an inner and an outer annular protrusion, respectively, which are intermeshing for joining both valve shells together. The advantage of this is the generation of a clamping force exerted onto the bulge of the diaphragm.
The radial transmission of clamping and tensile forces is furthermore supported by the fact that the bulge and the corresponding walls of both valve shells are provided with approximately identical annular, slanting surfaces. When the parts are dislocated, the force is transmitted without play to the bulge of the diaphragm.
For production technology and operational reasons, it is of advantage to design the bulge with radii as cross-sectional boundary.
Further advantages are achieved by equipping the first valve shell with an annual sealing lip, and the second valve shell with several stroke limiting nubs equally spaced on a pitch circle axially opposite the sealing lip. The sealing lip is located more centrally toward the openings of the diaphragm.
Production and operational safety of the parts to be assembled are further improved by the fact that both valve shell walls forming the outer, radial border of the cavity have an annular protrusion of semicircular cross-section.
The radial tensile strength is further supported by the fact that the sealing lip protrudes further from the valve shell wall than the annular, semicircular protrusion.
A design example of the invention is presented in the drawing and described in detail below.
The objects and advantages of the invention will be better understood upon a reading of the following specification read in conjunction with the accompanying drawings.